Piezoelectric accelerometer

Abstract

An accelerometer. At least some of the example embodiments include an accelerometer having a first piezoelectric element having a first polarization, the first piezoelectric element defining an upper surface and a second piezoelectric element having a second polarization, the second piezoelectric element defines a lower surface parallel to the upper surface of the first piezoelectric element; the first polarization being aligned with the second polarization. The accelerometer further includes a first mounting plate that defines a first aperture, the first and second piezoelectric elements extending through the first aperture such that the first mounting plate transects the first and second piezoelectric elements. The piezoelectric elements define a first cantilever portion on a first side of the first mounting plate, and the piezoelectric elements define a second cantilever portion on a second side of the first mounting plate opposite the first side.

What is claimed is: 
     
       1. An accelerometer comprising:
 a first piezoelectric element having a first polarization, the first piezoelectric element defines an upper surface; 
 a second piezoelectric element having a second polarization, the second piezoelectric element defines a lower surface parallel to the upper surface of the first piezoelectric element, and the first polarization aligned with the second polarization; 
 a first mounting plate that defines a first aperture; 
 
       the first and second piezoelectric elements extending through the first aperture such that the first mounting plate transects the first and second piezoelectric elements, the piezoelectric elements define a first cantilever portion on a first side of the first mounting plate, and the piezoelectric elements define a second cantilever portion on a second side of the first mounting plate opposite the first side;
 wherein the first mounting plate defines a periphery comprising: 
 a first arcuate curve portion; 
 a second arcuate curve portion disposed on opposite first arcuate curve portion; 
 a first chord connecting a first end of the first arcuate curve portion with a first end of the second arcuate curve portion; and 
 a second chord connecting a second end of the first arcuate curve portion with a second end of the second arcuate curve portion. 
 
     
     
       2. The accelerometer of  claim 1  further comprising:
 a second mounting plate that defines a second aperture, the second mounting plate spaced apart from the first mounting plate, and the second mounting plate parallel to the first mounting plate; 
 wherein the first and second piezoelectric elements extend through the second aperture such that the second mounting plate transects the first and second piezoelectric elements; and 
 wherein the first cantilever portion is disposed distally to the first mounting plate and the second cantilever portion is disposed distally to the second mounting plate. 
 
     
     
       3. The accelerometer of  claim 1  wherein the first mounting plate comprises a metallic member disposed abutting the first piezoelectric element, the first piezoelectric element bonded to the metallic member. 
     
     
       4. The accelerometer of  claim 3  wherein the metallic member and the first piezoelectric member are bonded by soldering the metallic member and a metallized layer on the upper surface of the first piezoelectric element. 
     
     
       5. The accelerometer of  claim 1  wherein the first and second piezoelectric elements are comprised of piezoelectric materials selected from the group consisting of:
 lead zirconate titanate (PZT); 
 barium titanate; 
 bismuth titanate; 
 lead titanate; 
 berlinite; and 
 polyvinylidene fluoride (PVDF). 
 
     
     
       6. The accelerometer of  claim 1  wherein the first mounting plate has a substrate of non-conductive material. 
     
     
       7. The accelerometer of  claim 1  wherein the second polarization has a sign opposite a sign of the first polarization. 
     
     
       8. The accelerometer of  claim 7  further comprising the accelerometer configured to produce an electrical signal in response to an acceleration component in a direction of sensitivity perpendicular to the upper surface, and the accelerometer configured to produce substantially no electrical signal in response to an acceleration component orthogonal to the direction of sensitivity. 
     
     
       9. The accelerometer of  claim 1  further comprising the accelerometer configured to produce an electrical signal in response to an acceleration component in a direction of sensitivity perpendicular to the upper surface, and the accelerometer is configured to produce substantially no electrical signal in response to pressure acting on the accelerometer. 
     
     
       10. The accelerometer of  claim 1  further comprising:
 a metallic member comprising a sheet of conductive material, a surface of the metallic member defines a first rectangle; 
 the first piezoelectric element coupled to a first side of the metallic member; 
 the second piezoelectric element coupled to a second side of the metallic member, the second side opposite the first side; 
 wherein the upper surface of the first piezoelectric element defines a second rectangle congruent to the first rectangle; and 
 wherein the lower surface of the second piezoelectric element defines a third rectangle congruent to the first rectangle. 
 
     
     
       11. The accelerometer of  claim 10  further comprising:
 a second mounting plate that defines a second aperture, the second mounting plate spaced apart from the first mounting plate, and the second mounting plate parallel to the first mounting plate; 
 wherein the first and second piezoelectric elements extend through the second aperture such that the second mounting plate transects the first and second piezoelectric elements; 
 wherein the first cantilever portion is disposed distally to the first mounting plate and the second cantilever portion is disposed distally to the second mounting plate; and 
 wherein the first and second mounting plates are constructed of a substrate of non-conductive material. 
 
     
     
       12. The accelerometer of  claim 11  further comprising:
 a housing that defines a first end, a second end opposite the first end, an interior volume, and a circular cross-section; 
 a cap coupled to and occluding the first end of the housing; 
 the mounting plates, piezoelectric elements, and metallic member disposed within the interior volume; 
 an end cap coupled to and partially occluding the second end; 
 a first electrical lead that extends through the end cap, the first electrical lead electrically coupled to the first piezoelectric element; and 
 a second electrical lead that extends through the end cap, the second electrical lead electrically coupled to the second piezoelectric element. 
 
     
     
       13. The accelerometer of  claim 1  wherein the first and second arcuate curve portions and the first and second chords are configured to modify a pressure-induced stress distribution in the piezoelectric sensing elements, and wherein, responsive to the modified pressure-induced stress distribution, a sensitivity of the accelerometer to acoustic pressure is reduced. 
     
     
       14. The accelerometer of  claim 13  wherein the sensitivity of the accelerometer is reduced responsive to polarization charges of the piezoelectric sensing elements having opposite sign and substantially equal magnitude.